1. Field of the Invention
The invention relates to optical fiber transmission lines and methods of making and operating such lines.
2. Discussion of the Related Art
Metropolitan and regional communication infrastructures often evolve and grow during their lifetime. Due to their evolution and growth, these infrastructures often eventually combine different technologies. The combinations of technologies can produce optical fiber transmission lines that are span-wise heterogeneous. In such lines, different ones of the optical transmission fibers produce significantly different optical power losses.
In an optical fiber transmission line, an amplifier couples sequentially related optical transmission fibers. The amplifiers produce adequate optical launch powers to compensate for power losses to optical signals in the immediately earlier optical transmission fiber of the line. Conventional amplification schemes provide substantially the same optical launch power to each optical transmission fiber. The constant value of the optical launch power is often found by modeling a generic homogenous optical fiber transmission line to simulate the real optical fiber transmission line.
Unfortunately, this modeling technique does not guarantee a large enough optical signal-to-noise-ratios (OSNRs) at delivery ends of all optical transmission fibers in a real optical transmission line that differs from the generic homogeneous optical fiber transmission line that was used to model the real line. In such real lines, some optical transmission fibers typically deliver optical signals with OSNRs that are too low for reliable further optical transmission. At the delivery ends of such optical transmission fibers, it is usually necessary to add an optical-to-electrical-to-optical (OEO) converter. The OEO converter can include a device that performs error correction on the resulting electrical signal sequence to reduce transmission error levels. After the error correction, the OEO converter optically transmits a partially or completely corrected data stream of optical signals to the next optical transmission fiber of the optical fiber transmission line. Such OEO conversions are typically costly and undesirable in optical fiber transmission lines.